The present invention is a process for the hydrogenation of chlorosilanes. The process comprises contacting a chlorosilane with aluminum and a hydrogen source selected from a group consisting of hydrogen gas and gaseous hydrogen chloride in the presence of a catalyst. The catalyst is selected from a group consisting of copper and copper compounds, tin and tin compounds, zinc and zinc compounds, and mixtures thereof.
Industrially significant methods for producing hydrosilanes involve, for example, the reaction of a halosilane with a metal hydride in the presence of a solvent as described in Kirk and Othmer, Encyclopedia of Chemical Technology; The Interscience Group, New York, N.Y, Vol. 12, p. 368, 1978. The preferred metal hydride reagents are LiAlH.sub.4 and NaAlH.sub.4. The reaction is reported to proceed quantatively at low system pressure and temperature. However, metal hydride reagents offer significant processing disadvantages. First, they are highly reactive and may oxidize exothermically to release explosive concentrations of hydrogen gas. Because of this, hydrogenation reactions with these reagents are typically carried out in solvents. The use of solvents presents a second disadvantage in that the solvent must be separated from the product. If solvents are not used, the metal may be stabilized by replacing a portion of the metal hydride ligands with bulky organic substituents. While this eliminates the solvent, it necessarily reduces the equivalent hydrogenation potential for the metal hydrides.
Non-metal hydride, non-solvent systems for hydrogenating halosilanes have also been reported. Hurd, U.S. Pat. No. 2,406,605, issued Aug. 27, 1946, disclosed the reaction of certain halosilanes with hydrogen or a hydrogen halide at an elevated temperature with a metal selected from a group consisting of aluminum, magnesium, and zinc. At temperatures of 400.degree. C. to 500.degree. C. and atmospheric pressure, Hurd determined that SiCl.sub.4 and MeSiCl.sub.3 could be reacted to SiHCl.sub.3 and MeHSiCl.sub.2 respectively. Hurd reported that the reaction of Me.sub.2 SiCl.sub.2 was generally unsuccessful, even at 500.degree. C.
Hatcher, U.S. Pat. No. 2,458,703, issued Jan. 11, 1949, reported a method of hydrogenating halosilanes using silicon as a chloride acceptor in a continuous high-pressure system. Hatcher reported that the silicon could reduce a halosilane in a hydrogen atmosphere when AlCl.sub.3 or AlBr.sub.3 was present.
Wagner et al., U.S. Pat. No. 2,595,620, issued May 6, 1952, reported that silicon could be used to reduce a chlorosilane with hydrogen at temperatures above about 400.degree. C. and the AlCl.sub.2 or AlBr.sub.3 required by Hatcher, supra, was not necessary.
Muetterties, U.S. Pat. No. 3,057,686, issued Oct. 9, 1962, reported a hydrogenation process where a halosilane was reacted with hydrogen and activated aluminum metal at superatmospheric pressure. Muetterties described the activated aluminum as a metal having an essentially oxygen free surface. The groups of compositions suitable for activating the aluminum as described by Muetterties were (1) metal hydrides, (2) mixtures of iodine and an alkyl halide in which the halogen has an atomic number of at least 17, and (3) trialkyl aluminum compounds.
Jenkner, U.S. Pat. No. 3,100,788, issued Aug. 13, 1963, reported a process for hydrogenation of halosilanes with hydrogen gas using sodium metal as the halogen receptor.
The present invention is a process for the hydrogenation of chlorosilane by a hydrogen source selected from a group consisting of hydrogen gas and gaseous hydrogen chloride. The process uses aluminum as the halogen receptor. The process does not require a solvent and can be run at near atmospheric pressure. The process employs a catalyst selected from a group consisting of copper and copper compounds, tin and tin compounds, zinc and zinc compounds, and mixtures thereof. Under the described process conditions, the catalyst provides for increased formation of silicon hydrogen bonds and increased chlorosilane conversion, when compared to the use of aluminum without catalyst. The catalyst also allows the process to be run at a lower temperature than that used for similar uncatalyzed processes.
Hydrosilanes prepared by the present process are useful intermediates in the formation, for example, of silicone polymers, elastomers, and resins.